1. Field of the Invention
This invention involves the production of numerous valuable chemicals using an innovative processing of sludges generated during primary, secondary and/or tertiary treatment of municipal, agricultural, and industrial wastewaters.
The produced chemicals include lipids and biodiesel (a renewable replacement to petroleum-based diesel), lecithin (a commercial nutrient and processing “building-block chemical” typically produced from eggs and soy oil), glycerol (a widely used chemical feedstock in many industrial processes), and a by-product that is much more digestible than typical influents to digestion processes at wastewater plants, due to the removal of the lipid fraction, which in turn will increase the rate and extent of digestion (resulting in greatly reduced sludge residual volumes requiring disposal and an increase in the quality of the resulting digested product).
2. Background of the Technology
The earth contains a wide variety of carbon reservoirs that can be harnessed to meet societal power requirements in the form of gaseous, liquid, and solid fuels, with liquid fuels being of most importance. The modem world has come to rely almost exclusively on fossil-based fuel reserves, a non-renewable resource, for production of liquid fuels. However, the cost and politics of being totally dependent on these reserves is getting progressively more expensive from both a strategic and sociological standpoint. A renewable source of fuels and other chemicals is required for meeting the future energy needs of the United States and the world.
Biodiesel represents an alternative to petroleum-based diesel fuel. Biodiesel is produced from renewable feedstocks. This fully renewable resource is most often produced from oil-yielding plants, such as soybeans and rapeseeds, or animal-based products, such as fats and oils captured during rendering, carcass processing, or recovery from frypits. Chemically speaking, biodiesel is a mixture of mono-alkyl esters of fatty acids, most often obtained from extracted plant oils and/or collected animal fats. The source of these fatty acids is lipids. Lipids are actually a class of chemicals found in plants, animals, microorganisms, and wastes derived from these sources. Lipids are not very soluble in water. Sewage sludge contains high levels of lipids, most often in the form of triglycerides, phospholipids, phosphoglycerides, sphinolipids, glycolipids, and fat-soluble vitamins.
Conversion of the plant oils and animal fats into biodiesel has been undergoing further development/optimization over the past several years. However, the base-catalyzed, methyl-transesterification of soybean oil has been the predominant production technique used within the United States. In Europe, rapeseed is the predominant feedstock used (Environment Canada, 2003; IA State, 2003). Commonly accepted biodiesel feedstocks include the oils from soy, canola, corn, rapeseed, and palm. New plant oils that are under consideration include mustard seed, peanut, sunflower, and cotton seed. In the case of animal fats, this feedstock is often called “yellow” grease. Grease collected from cooking establishments is called “brown” grease; however, this source can be made up of both plant and animal derived triglycerides. The most commonly considered animal fats include those derived from poultry, beef, and pork. The identification of less expensive sources of feedstock that can prove suitable for biodiesel production is very important to the continued expansion of biodiesel production and to less reliance on petroleum based fuels.
Wastewater biological treatment plants all produce waste sludges. In fact, vast quantities of sludges are produced on a daily basis. Ever-tightening environmental regulations, increases in disposal tipping fees, and rampant public resentment against these sludges and the current modes of disposal has placed operators of these facilities in a crisis situation to find novel techniques for managing these sludges. These sludges are composed of and derived from the biodegradation of essentially all liquid and solid matter fed into the treatment plants via the influent. Of key interest to this invention is the fact that lipids make up 2% to over 40% (dry weight basis) of the sludges produced from these treatment plants. Example sludges derived from these processes include primary sludge, grit residuals, skimmings, secondary sludge (waste sludge), sloughed biomass, biosolids, processed biosolids, and manure sludges from confined animal raising facilities. All of these sewage/manure-based sludges contain varying amounts of lipids.